I have three Dunlop Direzza Z1 Star Spec tires, 255/35-18, off my ZHP which is running a square setup.

Two measure a bit over 7/32, and the other one is just over 6/32. They were on the car for 12 months. The side of each toward the outside has a bit more wear, a bit less than an additional 1/32 in the next main groove over. The inside edges are essentially new while the outside ones have some wear (see pictures). I would mount the fresh edge to the outside.